1. Field of the Invention
This invention relates to an improvement in stereodemodulators. More specifically, it relates to stereodemodulators that obtain the left and right signals by sampling and holding the composite signal with sampling pulses having low duty ratios (abbreviated as sample-and-hold MPX demodulator hereafter).
2. Discussion of Prior Art
For improving the degree of separation in a stereodemodulator, a sample-and-hold MPX demodulator is known, which includes an oscillator which outputs a subcarrier having a frequency double that of the pilot signal in the composite signal, the subcarrier being phase-synchronized to the pilot signal. The prior art sample-and-hold MPX demodulator also includes circuitry for shaping the waveform of the oscillator output signal to obtain oppositely phased sampling pulses having low duty ratios and a sample-and-hold circuit which samples and holds the composite signal with the sampling pulses to obtain the left and right signals.
When stereodemodulation is performed by this prior art sample-and-hold MPX demodulator, separation is improved compared to a stereodemodulator that switches with oppositely phased subcarriers having duty ratios of 1:1. However, quantization distortion is greater in the high frequency range than in the low range during stereo reception due to the lower duty ratios of the sampling pulses. Thus, the prior art demodulator has a shortcoming in that the frequency characteristics in the high range are lowered. Further, since there is no such decrease in the high-frequency characteristics during monaural reception, an unnatural sensation is felt by a listener.